1. Field
Exemplary embodiments of the present invention relate to a resistive memory device, and more particularly, to a programming method of the resistive memory device.
2. Description of the Related Art
Generally, a data is recognized according to whether a fuse is cut by a laser or not in a resistive memory device. A fuse may be programmed in the stage of wafer. However, after the wafer is mounted on a package, it may be generally difficult to program the fuse.
An e-fuse is introduced and used to solve the problem. An e-fuse stores data by using a transistor which may change its electrical characteristic between a gate and a drain/source.
FIG. 1 is a schematic diagram of an e-fuse, which is formed of a transistor, operating as a resistor or a capacitor.
Referring to FIG. 1, the e-fuse is formed of a transistor T. A power source voltage is supplied to a gate G while a ground voltage is supplied to a drain/source D/S.
When a power source voltage of an ordinary level where the transistor T may operate is supplied to the gate G, the e-fuse can operate as a capacitor C. No current flows between the gate G and the drain/source D/S. However, when a high power source voltage, e.g., over-voltage where the transistor T may not normally operate, is supplied to the gate G, the gate oxide of the transistor T is destroyed to electrically short the gate G and the drain/source D/S, and then the e-fuse may operate as a resistor R. Current may flow between the gate G and the drain/source D/S. Based on the phenomenon, the data of an anti-fuse is recognized from the resistance value between the gate G and the drain/source D/S of the e-fuse. Herein, to recognize the data of the e-fuse, (1) the size of the transistor T has a large size to recognize the data without performing a sensing operation, or (2) an additional amplifier may be used to recognize the data of the e-fuse by sensing the current flowing through the transistor T having a small size. These two methods have limitation about integration degree, because the size of the transistor T constituting the e-fuse is required to be big, or each e-fuse has to be coupled with an amplifier for amplifying data.
FIG. 2 is a schematic diagram illustrating a memory device formed of an e-fuse, which is a resistive memory.
Referring to FIG. 2, the memory device includes a resistive memory M, a data line DL, a load 210, a sense amplifier 220, and a latch 230. Hereafter, an operation of programming the resistive memory M and an operation of reading data from the resistive memory M are described.
When the resistive memory M is programmed (or ruptured), a high voltage that can destroy a gate oxide of the gate G is supplied to the gate G of the resistive memory M. As a result, the resistive memory M operates as a resistor which has a relatively small resistance value, while a resistive memory M that may be not programmed operates as a capacitor which has a relatively great resistance value.
When the resistive memory M is read, a power source voltage of a level for a read operation is supplied to the gate G of the resistive memory M. As a result, a current path is formed from the resistive memory M to the data line DL and the load 210. Since the resistive memory M operates as a resistor when the resistive memory M is programmed, current flows through the load 210. Due to a voltage drop by the load 210, the level of a data voltage, which is a voltage of the data line DL, is increased. Since the resistive memory M operates as a capacitor when the resistive memory M may be not programmed, little current flows through the load 210. Therefore, the data voltage is in a low level near a ground level.
The sense amplifier 220 generates a data DATA by comparing the data voltage with a reference voltage VREF. The latch 230 latches the data DATA in response to a latch signal LAT_EN that is enabled after a predetermined time passes from a moment when the power source voltage is supplied to the gate G of the resistive memory M.
The gate oxide may be readily destroyed or hardly destroyed according to the characteristics of the resistive memory M. Therefore, after the resistive memory M is programmed, it is checked whether the resistive memory M is programmed normally by reading the data DATA, and when the resistive memory M may be not properly programmed, the resistive memory M is desirable to be programmed again.